The present invention relates to a lens barrel of an optical system that images an image of a photographic subject, an imaging apparatus that includes an imaging optical system using the lens barrel, and an information device.
A lens barrel constituting an imaging optical system in an imaging apparatus, such as a so-called digital camera or the like, is often subjected to a great impact due to being dropped accidentally, or by being hit against another object by a user, in a state of being attached to a body of the imaging apparatus, or in a state of being separated from a camera body as an interchangeable lens as an imaging optical system for a camera with an interchangeable lens such as a single-reflex camera or the like, or as a so-called core unit in which an imaging optical system and an image sensor part are integrated to be interchangeable.
That is, the above lens barrel has: an optical system that includes a plurality of lens groups each of which has equal to or more than one lens; and a cam mechanism that has a cam cylinder having a cam groove on a circumferential surface, and a lens-holding frame having a cam follower fitting the cam groove, and by means of the cam mechanism, the plurality of lens groups is driven along an optical axis direction, and the lens barrel constitutes a zoom lens or the like that changes a focal length, for example. In such a lens barrel, in many cases, measures to prevent the lens-holding frame from dropping off a cam connection when the above-described impact such as a dropping impact or the like is applied have been taken.
However, in a conventional lens barrel, in order to take measures against a dropping impact or the like, there are problems such that a component shape of each part becomes complex, and a diameter of a lens barrel increases. That is, in particular, in order to prevent a cam follower from dropping off a cam groove, taking a length, that is, a depth, of an engagement part of the cam follower and the cam groove to a sufficient degree has been carried out. In such a case, the diameter of a cam cylinder in which the cam groove is provided increases, as does the diameter of the lens barrel. Additionally, in the lens-holding frame having the cam follower, forming a shape that restricts deformation in the direction such that the cam follower drops off the cam groove due to an impact such as a dropping impact or the like has also been performed. In this case, the shapes of the lens-holding frame and a guide cylinder that limits the lens-holding frame to move only in the linear movement direction become complex, and the diameter of the lens barrel increases in order to form a shape that prevents deformation.
Thus, techniques that prevent disengagement of the cam connection due to the impact of the dropping impact or the like in the lens barrel are disclosed in, for example, Japanese patent application publication number 2002-277711, Japanese patent application publication number 2010-164695, and so on.
That is, in order that a cam engagement part does not easily drop off due to an external force in the optical axis direction that is applied to the lens barrel in an extending-type lens barrel, Japanese patent application publication number 2002-277711 discloses that a lens barrel includes: a lens-holding cylinder in which a cam follower part and a linear movement key part are provided; a cam cylinder in which a cam groove part that engages with the cam follower part and provides a driving force in the optical axis direction to the lens-holding cylinder is provided; and a guide cylinder in which a linear movement guide groove part that engages with the linear movement key part and guides the lens-holding cylinder in the optical axis direction is provided, and in the above lens barrel, a claw-shape part that protrudes in a circumferential direction is formed in the linear movement key part, and on an end surface in the circumferential direction of the linear movement guide groove part, a rail part with which the claw-shape part is capable of engaging in the diameter direction and which extends in the optical axis direction is formed, which prevents the cam follower part from dropping off to move in a diameter direction of the lens barrel with respect to the cam groove part in a case where an external force in the optical axis direction is applied to the lens-holding cylinder.
Given such a constitution, it is possible to reliably enhance any impact resistance of the lens barrel; however it is not possible to completely resolve problems such as the component shape of each part becoming complex, and the diameter of the lens barrel increasing.
Additionally, Japanese patent application publication number 2010-164695 discloses that a projection part that forms a cylindrical surface projecting along the optical axis direction on a photographic subject side is provided in a shutter unit arranged in a lens barrel part, and the projection part is inserted into an inner side of a lens-holding cylinder arranged closer to the photographic subject side than the shutter unit, and therefore deformation of the lens-holding cylinder is prevented.
With such a constitution, deformation resistance is enhanced, and impact resistance is improved; however, the position of the lens-holding cylinder is still limited, and the component shape of the shutter unit can become complex; and therefore, it is not possible to completely resolve problems such as an decrease in versatility of the shutter unit, and an increase in the diameter of the lens barrel.